A serializer/deserializer (SERDES) circuit typically comprises circuitry configured to transmit parallel data over a serial communications channel. Typically, a multiplexer receives parallel data and converts the parallel data to serial data. A transmitter receives serial data and transmits the serial data over a serial communication channel. A receiver receives the serial data and forwards the serial data to a demultiplexer, which recreates and attempts to recover the original parallel data. Loopback testing is one of a number of different testing methodologies for testing transmitters and receivers associated with a SERDES circuit.
A SERDES circuit may be configured as a single channel SERDES, or as a parallel channel SERDES. In single channel SERDES circuits, loopback mechanisms were previously implemented to connect the receive (RX) channel to the transmit (TX) channel. Since, in a single channel SERDES, these circuits were located adjacent to each other, the connection was very simple. However for parallel SERDES architectures, the distance between the RX and TX devices, as well as the number of channels, complicates loopback testing.
Therefore, it would be desirable to have a way to implement loopback testing in a parallel SERDES architecture.